Deformable self-supporting explosive composition



United States Patent 2,999,743 DEFORMABLE SELF-SUPPORTING EXPLOSIVE COMPOSITION Cyril James Breza, Thorofare, and Clyde Oliver Davis, Wenonah, N.J., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Aug. 17, 1960, Ser. No. 46,044

5 Claims. ('Cl. 52-5) 2,999,743 l atented Sept. 12, 1961 2 For example, if the dispersing agent is removed from the mixture before formation 'of the desired shapes, the rubber explosive mixture 'is formed into the desired shapes, for'example into sheets by rolling, onlywith great difliculty, if at all, due to the resiliency of this mixture. On the other hand, when the mixture containing the dispersing agent is worked up into the required shapes, for example by casting or extrusion,'subsequent evaporation of this agent from the units results in undesirable void spaces in .the units, which voids cause dee sensitization and nonuniform density. The problem of position comprising a cap-sensitive crystalline high explosive compound admixed with a. binding agent and to a method of fabricating the composition.

This application is a continuation-in-part of our prior application Serial No. 666,221, filed June 17, 1957, now abandoned.

For many applications of explosives, the use of crystalline high explosive compounds, such as PETN or RDX, in the form of self-supporting units rather than as crystals or granules would be highly desirable. For example, for the method of joining metallic elements described in U.S. Patent 2,367,206, issued January 16, 1945, sleeves of explosives are provided by containing the charge of granular high explosive ina rigid annular container made of paper and the like. These containers must be slipped over the metallic element and a metal I sleeve and, thus, are subjected to considerable stress which, in many cases, causes rupture of the necessarily rigid container. Moreover, because of their rigidity, many of these explosive units break during storage and transport. provision of a deformable self-supporting unit would be very advantageous. Moreover, the desirability of using flexible sheets of explosive which are cohesive enough to be cut, molded, or otherwise deformed to metal as in the method of work-hardening described in detail in U.S. Patent 2,703,297 issued March 1, 1955, is expressed in this patent. In shaped charge perforators, the substitution of cohesive, self-supporting contoured shapes of explosive for the presently used charges of explosive Obviously, elimination of this container and which are pressed into a casing would facilitate the'preparation of such perforators. Such self-supporting explosive units, however, are not presently available.

Heretofore, many attempts have been made to prepare However, the results such applications. Wax also has been added to high explosives in efforts to prepare self-supporting explosive units. However, the quantity of wax required to provide the necessary cohesiveness in these units desensitizes the units with the result that they cannot be shot.

In further efforts to prepare self-supporting explosive compositions, rubber has been incorporated into crystalline high explosives. However, not only is a homogeneous mixture of pure rubber and the explosive difficult to prepare, even when a volatile dispersing agent is used,

due to the tendency of the components of the mixture to segregate, but also the resultant mass'is diflicult to work.

nonuniform density is further complicated by thefact that the consistency of the mixture before extrusion or casting cannot be maintained uniform. Moreover, the resiliency of rubber explosive sheets, when and if obtained, is such that the sheet will not retain the requisite deformation but will spring back to the original shape. Thereby, the use of such sheets is dilficult, if not impossible, in many applications of sheet explosive.

Accordingly, an object of the present invention is to provide a self-supporting deformable explosive composition prepared in a simple and safe manner. Another object of the present invention is to provide a self supportingjexplosive composition which can be formed readily into explosive units of the desired shape and having uniform density. A further object of the present invention is to provide a method by which high-density sheets of a self-supporting deformable explosive composition can be fabricated readily and safely. A further object of the present invention is to provide self-support ing explosive units which can be deformed and will remain in the desired deformed state.

We have found that the foregoing objectsmay be achieved when we provide an explosive composition comprising a cap-sensitive crystalline high explosive compound, such as pentaerythritol tetranitrate (commonly referred to in the explosives arts as PETN) or cyclotrimethylenetrinitramine (commonly referred to in the explosives arts as R1DX), and a binding agent consisting of an organic rubber and a thermoplastic terpene hydrocarbon resin.

In accordance with the present invention, 92.5 to 70 parts by weight of a cap-sensitive crystalline high exmixture by evaporation. The resulting .dry solvent free composition is cohesive and formable and,-thus, is easily and safely worked by pressing or rolling to form explosive sheets or other shapes having a high density and a high detonation velocity.

The following examples serve to illustrate specific embodiments of the explosive composition of the present invention. However, they will be understood to be illustrative only and not as limiting the invention in any manner. Unless designated otherwise, the parts in the examples are parts by weight. The thermoplastic terpene hydrocarbon resin used in all the examples was Piccolyte a commercially available material and composed essentially of polymers of fl-pinene. Of course, as is evident, other thermoplastic terpene hydrocarbon resins could [be substituted for the Piccolyte.

EXAMPLE 1 Water-wet PETN in the amount of 283 parts (dry basis) was mixed with parts of a hexane solution containing 50 parts of a 50/50 mixture, by weight, of butyl rubber and the terpene resin Piccolyte 3-10 and 8-70 grades) over a period of 10 minutes with vigorous agitation Then, the water present on the surface of the mass was decanted, and the mass, which was glue-like and sticky, was removed from the mixer and. spread out on a tray to air-dry overnight. After the water and hexane were evaporated, the PETN-binding agent mixture (85/ 15, weight ratio), which was no longer sticky, was rolled into sheets between brass rollers.

The sheets had a density of 1.45 grams per cc. and had an impact sensitiveness, as determined by the standard drop test (S-kg. weight), of 12 inches (50% detonation point). The sheets could be initiated by No. 6 blasting caps, and the velocity of detonation was 7200 meters per second. In appearance, the sheets were strong, flexible, and their resilience was so slight that when bent they retained their deformed shape. After one months storage (normal and low temperature), no change occurred in the sheets. Immersion of the sheets in water psi.) had no efliect upon them.

EXAMPLE 2 Two mixes were prepared in accordance with the method of Example 1, with the exception that the proportions of elastomer and terpene resin in the binding agent were varied. The properties of the sheets formed from these mixes are listed in the following table.

Table 1 Ratio of Impact Sen- Velocity of Mix Elastomer/ Density sitivcness Detona- Resin in (g./cc.) (Drop Test tion (m./

Binder in Inches) sec.)

1 Tough sheet with good flexibility, slightly stiff and slightly resilient 2 Tough sheet with good flexibility, limp and slightly sticky, no resilience Sheets made from both mixes could be initiated by No. 6 caps.

EXAMPLE 3 A number of mixes were prepared by the aforedescribed method from PETN and a 50/50 mixture of butyl rubber and the terpene resin. In these mixes, the proportions of PETN to hinder were varied as shown in the following table which summarizes the properties of the sheets prepared from these mixes.

All the sheets were strong and flexible with little resiliency and could be initiated by No. 6 caps.

EXAMPLE 4 Sheets were rolled from a mix prepared as described in Example 1 with the exception that polyisobutylene (commercially available as Vistanex) was substituted for the butyl rubber. The mixture was rolled out into sheets which were strong and flexible and had a density of 1.41 grams per cc. In the standard drop test (5 kg.

weight), the 50% detonations point of the sheet was 11 inches. The detonation velocity of the sheet was 6700 meters per second, and the sheet could be initiated by No. 6 caps.

EXAMPLE 5 An 85/15 mixture of RDX and binding agent (50/ 50 'xture of butyl rubber and the terpene resin) was prepared by the method of Example 1. The mixture was 4 rolled into sheets weighing 4 grams per square inch and having a density of 1.48 grams per cc. These sheets were strong and flexible and detonated at a velocity of 7100 meters per second. In the drop test (5 kg. weight) made on these sheets, the 50% detonations point was 26 inches. The sheets were initiated by No. 6 caps.

EXAMPLE 6 A flexible sheet explosive composition was prepared as in Example 1 consisting of 70% by weight PETN (dry basis) and 30% of the 50/50 butyl rubber-terpenc resin binder. In this example, the PETN used was of a particle size within the range of 01-10 microns with an average maximum particle dimension of 0.1-2.0 microns.

The sheet had a density of 1.21 grams/cc and had an impact sensitiveness, as determined by the standard drop test (5 kg. weight), of 56 inches (50% detonation point). The sheet could be initiated by a No. 6 blasting cap, and the velocity of detonation was 6500 meters/sec. The sheet was strong, flexible, retained any shape into which it was deformed, and exhibited good storage characteristics.

As may be seen by reference to the foregoing examples, the addition of an elastomer and a thermoplastic terpene hydrocarbon resin to a cap-sensitive crystalline high explosive compound results in a mass which is cohesive, flexible, and of only slight resilience. Due to these properties, the mass can be worked up into the desired form, for example, sheets, in a simple manner and without difl'iculty. The resultant forms have the cohesiveness, flexibility, and nonresilience required for their use in many applications of explosives, e.g. the previously mentioned joining method, and in addition, are water resistant, unaffected by storage under normal conditions or at low temperatures, and of high density.

Although the rolling of the mass into sheets has been exemplified and is claimed, the mass also can be worked up into other forms, for example the contoured shapes required for shaped charge perforators, by other processes such as molding. Moreover, the nature of the explosive mass is such that it can be formed into sheets by methods other than rolling, i.e. by slicing or cutting of the mass.

The high explosive component constitutes 92.5 to 70% of the explosive composition. The use of greater amounts of this component results in forms lacking the desired cohesiveness and having a tendency to crack, whereas the use of lesser amounts of the high explosive results in forms which will not detonate. Compositions within the present invention having lower proportions of the explosive will usually contain the explosive in a finely divided form to insure detonatability. When the proper proportions of high explosive and binder are used, the sheets or other forms can be initiated by commercially available blasting caps and will detonate at velocities in the order of 7000 meters per second. The use of PETN, an organic nitrate, and RDX, a nitrarnine, which are representative cap-sensitive crystalline high explosive compounds, as this component of the explosive composition has been exemplified. However, the use of other cap-sensitive crystalline high explosive compounds is equally feasible. For example, other organic nitrates, such as nitromannite, and other nitrarnines such as HMX (cyclotetramethylenetetranitra- 'mine) and ethylenedinitramine, also can be used. Moreover, a mixture of such compounds or of a high explosive compound such as PETN and a less sensitive material such as ammonium nitrate is suitable.

The binding agent constitutes 7.5 to 30% of the explosive composition andcomprises a mixture of 25-75% of an organic rubber and 7525% of a thermoplastic terpene hydrocarbon resin. As shown in Example 2, increasing the proportion of the rubber increases the resilience of the explosive composition, and when the rubber constitutes more than 75% of the binding agent the composition is, unsatisfactorily resilient. On the other hand, the use of less than 25% of the rubber in the binder gives a composition which is very ditficult to form and lack strength and cohesiveness.

Butyl rubber and polyisobutylene were used to prepare the mixes described in the examples because they are representative and readily obtainable rubber products. However, any organic rubber may be used in preparing the explosive composition of the present invention. Such materials include natural rubber and synthetic rubbers such as GR-S rubber, neoprene, polysulfide rubber (commercially available as Thiokol), Buna N, chlorosulfonated polyethylene (commercially available as Hypalon S-2), etc.

Thermoplastic terpene resins are readily available com mercially in either solid form or in solution. These resins are prepared in a well-known manner by the polymerization of ,B-pinene containing minor amounts of ozpinene and dipentene in the presence of a Friedel-Crafts catalyst, such as anhydrous aluminum chloride, according to the techniques described in detail by Kirk-Othmer, Encyclopedia of Chemical Technology, Interscience Publishers, Inc. (1954), vol. 13, pages 702-3. The resins have the empirical formula (C H wherein n represents the degree of polymerization. The latter may be varied over a wide range to yield polymers of low or relatively high average molecular weights. Resins having average molecular weights as high as 1200 to 1250 are known; such resins having a softening point in the range of 125-135 C. The softening point is, of course, a function of average molecular weight and thus characterizes a particular resin this regard. The various grades of the well-known Piccolyte resins are designated in this manner and the softening points of Piccolyte S-10 and Piccolyte" S-7O thus are 10 C. and 70 C., respectively. These particular Piccolyte resins are very convenient to work with and yield an explosive composition of the type described having excellent workability and other physical properties in line with the objectives of the invention. The use of these particular resins is by no means critical to the invention, however, and the novel compositions of the present invention may be prepared with any grade of Piccolyte or other hydrocarbon terpene resin.

Although a variety of methods can be used to prepare sheets of the explosive composition, the method described in Example 1, i.e. admixing the high explosive with a solution of the rubber and resin, drying the mixture to drive off the solvent, and thereafter rolling the dried mass, is simple and gives very good results, especially with respect to the uniformly high density obtained in the sheets, and thereby is preferred. Any one of a wide variety of hydrocarbon solvents can be used in mixing the composition, and the mixture can be dried in a number of ways, for example air drying at ambient temperatures or hot air drying on trays or by supplying heat directly to the mixer to evaporate the solvent.

An attendant advantage of the explosive composition of the present invention resides in the fact that water is incompatible with the mixture of rubber and resin and thus separates out of the mixture and can be removed by decantation or suction, residual quantities 'of water being removed by evaporation during the drying of the mixture. Thus, the high explosive can be added in the water-wet state, in which state it is inherently safer than in the dry form. Of course, when hygroscopic components are used in the composition, the presence of water is to be avoided.

An additional feature of the explosive composition of the present invention is the fact that by application-of a thin layer of a pressure-sensitive adhesive to the surface of the formed unit, e.g. the sheet, the unit will adhere to surface of another object. This feature makes the use of the composition especially advantageous in an application such as the afore-discussed metal hardening method. For

example, sheets could be formed from the composition, a

6 layer of the adhesive could be placed on one surface of the sheets, and then a layer of crepe release paper could be placed upon the adhesive. When one of these sheets was to be used in metal hardening, the release paper 7 would be removed and the adhesive surface of the sheet would be pressed against the surface of the metal to be hardened to give a strong bond between the sheet and the metal.

Although the invention has been described in detail in the foregoing, it will be apparent to those skilled in the art that many variations are possible Without departure from the scope of the invention. We intend, therefore, to be limited only by the following claims.

We claim:

1. An explosive composition consisting essentially of a cap-senstive crystalline high explosive compound selected from the class consisting of the organic nitrates and nitramines admixed with a binding agent consisting of 25-75% by weight of an organic rubber and -25% by weight of a thermoplastic terpene hydrocarbon resin, said high explosive compound constituting 9'2.5-7(l% by Weight of said explosivecomposition, said composition having the ability to deform in shape when subjected to mechanical pressure or manipulation and to hold itself in any shape into which it is thus formed when the pressure is released whereby the composition may be molded or shaped at room temperature into a self-supporting physical form of any desired size and configuration.

2. An explosive composition according to claim 1, wherein the high explosive compound is a member of the group consisting of pentaerythritol tetranitrate and cyclotrimethylenetrinitramine.

'3. An explosive composition according to claim 1, wherein the organic rubber is a member of the group consisting of butyl rubber and polyisobutylene.

4. An explosive composition in sheet form comprising a cap-sensitive crystalline high explosive compound selected from the class consisting of the organic nitrates and nitramines admixed with a binding agent consisting of 25-75% by weight of an organic rubber and 75-25% by weight of a thermoplastic terpene hydrocarbon resin, said high explosive compound constituting 92.5-70% by weight of said explosive composition, said composition having the ability to deform in shape when subjected to mechanical pressure or manipulation and to "hold itself in any shape into which it is thus formed when the pressure is released whereby the composition may be molded or shaped at room temperature into a self-supporting physical form of any desired size and configuration.

5. A method of fabricating a self-supporting defonm able explosive composition in sheet form which consists of intimately admixing 92.5-7(l% by weight of a capsensitive crystalline high explosive compound selected from the class consisting of the organic nitrates and nitramines with 75-30% by weight of a binding agent consisting of 25-75% by weight of an onganic rubber and 75-25% by weight of a thermoplastic terpene hydrocarbon resin, said binding agent being in solution, removing the solvent from the mixture by evaporation, and thereafter rolling the solventfree mixture into sheets.

References Cited in the file of this patent UNITED STATES PATENTS 59,888 Abel Nov. 20, 1866 2,147,698 Goodyear Feb. 21, 1939 2,471,851 Wright et a1. May 31, 1949 2,541,389 Taylor Feb. 13, 1951 2,768,072 Stark Oct. 23, 1956 I OTHER REFERENCES Kirk and Othmeri Encyclopedia of Chemical Technology, vol. 13, page 701, 1954. I 

1. AN EXPLOSIVE COMPOSITION CONSISTING ESSENTIALLY OF A CAP-SENSITIVE CRYSTALLINE HIGH EXPLOSIVE COMPOUND SELECTED FROM THE CLASS CONSISTING OF THE ORGANIC NITRATES AND NITRAMINES ADMIXED WITH A BINDING AGENT CONSISTING OF 25-75% BY WEIGHT OF AN ORGANIC RUBBER AND 75-25% BY WEIGHT OF A THERMOPLASTIC TERPENE HYDROCARBON RESIN, SAID HIGH EXPLOSIVE COMPOUND CONSTITUTING 92.5-70% BY WEIGHT OF SAID EXPLOSIVE COMPOSITION, SAID COMPOSITION HAVING THE ABILITY TO DEFORM IN SHAPE WHEN SUBJECTED TO MECHANICAL PRESSURE OR MANIPULATION AND TO HOLD ITSELF IN ANY SHAPE INTO WHICH IT IS THUS FORMED WHEN THE PRESSURE IS RELEASED WHEREBY THE COMPOSITION MAY BE MOLDED OR SHAPED AT ROOM TEMPERATURE INTO A SELF-SUPPORTING PHYSICAL FORM OF ANY DESIRED SIZE AND CONFIGURATION. 